The present disclosure relates to an imaging apparatus, a current/voltage conversion circuit, and an imaging method.
In the past, a transmission X-ray imaging technique in which the internal state of a living body or object is observed by the applying X-rays to the living body or object and detecting transmitted X-ray for visualization has been known. In the transmission X-ray imaging technique, a photographic plate or photograph film has been used to detect the transmitted X-ray. In recent years, however, a flat panel detector has been developed extensively (see, for example, Japanese Patent Application Laid-open No. 2010-098621).
The flat panel detector employs one of two methods: a direct conversion method in which an X-ray is directly converted into an electric signal; and an indirect conversion method in which an X-ray is converted into an optical signal before the optical signal is converted into an electric signal. With any of the methods, it does not need to use a film, and it is possible to improve image quality and support diagnosis using digital image processing. In addition, the flat panel detector has such advantages that electronic filing or networking of a transmitted X-ray image can be easily performed, for example, and is expected to be used in various fields.
FIG. 21 is an equivalent circuit schematic showing an example of an image sensor and a current/voltage conversion circuit constituting a flat panel detector. The flat panel detector shown in FIG. 21 includes a plurality of (M×N) image sensors 230 arranged in a two-dimensional matrix pattern in an X-direction and Y-direction, and is configured to convert an incident X-ray into current directly (direct conversion method) or indirectly (indirect conversion method).
The plurality of (M) image sensors 230 arranged in the X-direction are connected to one current/voltage conversion circuit 240 via a switching circuit 232 and a row wiring 233. The current/voltage conversion circuit 240 is configured to successively convert current input from each image sensor into voltage. In FIG. 21, the reference number 231 represents a parasitic capacitance (capacity value: Cpd) of the image sensors 230.
The current/voltage conversion circuit 240 is a well-known current/voltage conversion circuit (a kind of integration circuit) including an operational amplifier 241, a capacitor unit 242 (capacity value: Cint), and a short circuit 243 having a reset switching circuit 244. To a non-inversion input unit of the operational amplifier 241, a reference voltage Vref is input. The non-inversion input unit of the operational amplifier 241 is connected to the row wiring 233. The capacitor unit 242 and the short circuit 243 are connected to each other in parallel, and are connected to an inversion input unit and an output unit of the operational amplifier 241.